As electronic instruments are recently becoming smaller and lighter and exhibiting more excellent performances in the market, the degree of integration in semiconductors increases, and the surface mounting in semiconductor packages is promoted. Moreover, it is considered to be important for activities of corporations that the influences on the global environment are considered, and it is required that the use of lead which is a harmful substance be entirely prohibited by 2006 except specific applications. However, since the melting point of lead-free solder is higher than conventional lead/tin solder, the temperature during the mounting with solder reflow such as infrared solder reflow and dipping into a solder will be elevated to a temperature as high as 240 to 260° C. from 220 to 240° C. in the conventional soldering. Due to the elevation of the temperature during the mounting, a problem arises in that cracks tend to be formed in the resin portion during the mounting, and assurance of reliability becomes difficult. Moreover, with respect to a lead frame, application of a lead frame treated by the nickel palladium plating in advance in place of the exterior solder plating is promoted from the standpoint of the necessity of removing lead from the exterior solder plating. Since the nickel palladium plating has poor adhesion with conventional materials for encapsulating, cleavage tends to take place at the interface during the mounting, and cracks tend to be formed in the resin portion.
The above problems due to the elevation of the temperature during the mounting have been overcome by application of epoxy resins and curing agents exhibiting small absorption of water to improve the heat resistance in soldering (for example, Patent References 1, 2 and 3). However, the epoxy resin composition exhibiting small water absorption and small modulus such as those described above has a small crosslinking density, and the molded article is soft immediately after curing. This causes a problem in the molding property in that the resin adheres to a mold in the continuous production, and the productivity decreases.
As the effort to improve the productivity, application of a mold release exhibiting an excellent releasing effect is proposed (for example, Patent Reference 4). However, a problem arises in this case in that the mold release exhibiting an excellent releasing effect inevitably tends to bloom out on the surface of the molded article, and the appearance of the molded articles is markedly deteriorated during the continuous production. It is proposed that a silicon compounds having a specific structure is added as a means to obtain an epoxy resin composition providing molded articles exhibiting excellent appearance (for example, Patent References 5 and 6). However, this technology causes a problem in that filling of the resin composition is insufficient, and the productivity is decreased since the releasing property from a mold is insufficient, and air vents are clogged due to attachment of the resin to the air vents. As described above, an epoxy resin composition for encapsulating semiconductor devices which can overcome the drawbacks on the heat resistance in soldering, the releasing property from a mold, the continuous molding property, the appearance of the molded article and the fouling on the mold, has been required.
[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 9 (1997)-3161 (pages 2 to 5)
[Patent Reference 2] Japanese Patent Application Laid-Open No. Heisei 9 (1997)-235353 (pages 2 to 7)
[Patent Reference 3] Japanese Patent Application Laid-Open No. Heisei 11 (1999)-140277 (pages 2 to 11)
[Patent Reference 4] Japanese Patent Application Laid-Open No. 2002-80695 (pages 2 to 5)
[Patent Reference 5] Japanese Patent Application Laid-Open No. 2002-97344 (pages 2 to 10)
[Patent Reference 6] Japanese Patent Application Laid-Open No. 2001-310930 (pages 2 to 8)